An as-solidified structure of an Al-based ribbon sample produced by the melt-spinning technique was studied by x-ray diffractometry and transmission electron microscopy. The addition of Pd to Al-Y-Ni-Co alloys caused formation of the highly dispersed primary α-Al nanoparticles about 3–5 nm in size homogeneously embedded in the glassy matrix upon solidification. The first direct observation of microstrain and dislocations quenched in nanoparticles with a size below 7 nm is provided.

A metallic glass/porous tungsten bi-continuous phase composite was prepared by pressure infiltration whose quasi-static compressive stress and strain to macroscopic failure are much higher than those of all the previous tungsten-reinforced metallic glass matrix composites. It deserves to be mentioned that because of its high-yield strength and high elastic strain limit, metallic glass seems to be used as the reinforcement to strengthen the crystalline materials in the bi-continuous phase composite materials.

We report the fabrication of Mg-doped NdBCO generic seed crystals, which have been developed recently for the fabrication of any rare earth (RE) based (RE)-Ba-Cu-O single-grain superconductor, with a wide range of Nd1+xBa2-xCu3-yMgyO7-δ compositions. Three basic characteristics of the seed crystals required for effective seeding of bulk (RE)BCO materials were studied in detail. We report the chemical, crystallographic, microstructural, and superconducting properties of the seeds and demonstrate clearly their potential to process various (RE)BCO superconductors in single-grain form. The melting point, volume fraction of Mg-rich inclusions in the bulk microstructure, and the chemical composition of the Nd1+xBa2-xCu3-yMgyO7-δ superconducting matrix of the seed crystals were studied as a function of initial MgO content. Finally, the suitable range of MgO-content within the generic seed crystal that controls effectively the orientation of the seeded grain without compromising its superconducting properties relative to those of the Mg-free compound is identified based on the wide range of seed crystal compositions investigated.

The work of indentation is investigated experimentally in this article. A method of using the elastic energy to extract the elastic modulus is proposed and verified. Two types of hardness related to the work of indentation are defined and examined: Hwtis defined as the total work required creating a unit volume of contact deformationand Hwp is defined as the plastic work required creating a unit volume of plastic deformation; experiments show that both hardness definitions are good choices for characterizing hardness. Several features that may provide significant insights in understanding indentation measurements are studied. These features mainly concern some scaling relationships in indentation measurements and the indentation size effects.

Deformation and fracture behavior of Zr41.25Ti13.75Ni10Cu12.5Be22.5 bulk metallic glass and its composite containing transverse tungsten fibers in compression were investigated. The monolithic metallic glass and the tungsten fiber composite specimens with aspect ratios of 2 and 1 are shown to have essentially the same ultimate strength under compression. The damage processes in the bulk metallic glass composite consisted of fiber cracking, followed by initiation of shear band in the glassy matrix mainly from the impingement of the fiber crack on the fiber/matrix interface. The site of the shear band initiation in the matrix is consistent with the prediction of finite element modeling. Evidence is present that the tungsten fiber can resist the propagation of the shear band in the glassy matrix. However, the compressive strain to failure substantially decreased in the present composite compared with the composites containing longitudinal tungsten fibers. Finally, the two composite specimens fractured in a shear mode and almost all the tungsten fibers contained cracks.

Here, we report investigations on the instability in luminescence of bare (trioctylphosphine oxide [TOPO]-stabilized) and CdS-capped CdSe particles under infrared radiation. During thermal annealing under radiation, the formation of oxide layers on the surfaces of the particles create defect states. Consequently, there is a reduction in particle size. These two effects control the light output from the samples. We make a quantitative comparison of the stability of bare CdSe and core-shell-type CdSe-CdS particles during annealing under infrared radiation. Using diffusion theory, we show that the volume of the oxide layer, adhered to the crystallites, plays a dominant role in controlling the luminosity of the particles.

Powders of Ba0.65Sr0.35TiO3 have been prepared by solution-based and conventional mixed-oxide routes. Powders made by freeze-drying a precursor solution of mixed catecholate complexes of BaTiO3 and SrTiO3 had the smallest particle size, but secondary grain growth during sintering negated the anticipated benefits of the nano-sized powder in relation to ceramic densification and microstructural control. Addition of manganese oxide suppressed secondary grain growth for catecholate powders, allowing 97% dense ceramics to be produced at a sintering temperature of 1300 °C, with grain sizes of ≤5 μm. Doped mixed-oxide samples continued to show secondary grain growth, leading to coarse microstructures with grain sizes ≤100 μm after sintering at 1400 °C. Curie peaks for catecholate samples were sharper than those for mixed-oxide samples, suggesting a more uniform distribution of Ba and Sr ions in the powders. Difficulties were encountered in controlling the (Ba + Sr)/Ti ratio of powders made by an oxalate solution-precipitation route.

The surface tension of the Fe-P binary liquid solution was computed using a Butler's model in wide composition and temperature ranges by adopting the activity coefficient data that were evaluated from the phase diagram calculation. In the surface tension modeling, the Fe-P binary system was assumed as the Fe-Fe3P pseudo-binary system. The results of the computation were critically compared with the experimental data of the literature considering the effects of the size of the adsorbed elements and the interactions among them. The results of the computation at 1823 K showed good agreement with the selected experimental data of the literature in a wide composition range from 0 to 15 mass%P. Furthermore, the results of the computation at 0.5 mass%P showed good correlation with the selected experimental data of the literature in a wide temperature range from 1823 K to 1923 K.

The structure and phase of the Al2O3 scale that forms on an Fe3Al-based alloy Fe-28Al-5Cr (at.%) was investigated by transmission electron microscopy and photoluminescence spectroscopy. Oxidation was performed at 900 °C and 1000 °C for up to 190 min. Transmission electron microscopy revealed that single-layer scales were formed after short oxidation times. Electron diffraction was used to show that the scales are composed of nanoscale crystallites of the θ, γ, and α phases of alumina. Band-like structure was observed extending along three 120°-separated directions within the surface plane. Textured θ and γ grains were the main components of the bands, whereas mixed α and transient phases were found between the bands. Extended oxidation produced a double-layered scale structure with a continuous α layer at the scale/alloy interface and a γ/θ layer at the gas surface. The mechanism for the formation of Al2O3 scales on iron aluminide alloys is discussed and compared with that for nickel aluminide alloys.

A nano-sized amorphous layer embedded in an atomic simulation cell was used to study the amorphous-to-crystalline (a-c) transition and subsequent phase transformation by molecular-dynamics computer simulations in 3C–SiC. The recovery of bond defects at the interfaces is an important process driving the initial epitaxial recrystallization of the amorphous layer, which is hindered by the nucleation of a polycrystalline 2H–SiC phase. The kink sites and triple junctions formed at the interfaces between 2H– and 3C–SiC provide low-energy paths for 2H–SiC atoms to transform to 3C–SiC atoms. The spectrum of activation energies associated with these processes ranges from below 0.8 eV to about 1.9 eV.

Zirconia oxynitride rare-earth-doped pigments were prepared by ammonolysis of the zirconium rare-earth oxides, previously synthesized using the citrate complexation/calcination route. Different coloration has been obtained, the intensity of which is a function of the nitrogen amount in the case of the oxynitrides; in the case of the oxides, both color and intensity depend on the doping amount of rare earth. The obtained phases, Zr(1−x)CexO2, Zr(1−x)RxO(2−x/2)□x/2, with R = Eu or Er and Zr(1−x)RxO(2−x/2−3/2y)Ny□x/2■y/2 (R = Ce, Eu, and Er), have been characterized by x-ray powder diffraction, scanning electron microscopy, and reflectance spectra data. These results show that the phases with minor rare-earth concentration adopt a baddeleyite-type structure, with a monoclinic symmetry, space group P21/c. By increasing the rare-earth doping, the obtained phases crystallize with the fluorite structure with tetragonal (P42/nmc) or cubic symmetry (Fm¯3m). On the other hand, the study of the magnetic properties of the oxides and oxynitrides indicate a paramagnetic behavior, and in the case of the cerium oxide, the nitridation process produces the reduction from Ce4+ to Ce3+. Diffuse reflectance data and CIE-LAB color coordinates suggest that these ceramics based on nitrogen containing zirconia are expected to be promising candidates as new ecological inorganic pigments.

The silver-copper oxide–based reactive air brazing technique was developed as a method of joining complex-shaped ceramic parts. To investigate the viability of this approach for high-temperature application, a series of air-brazed alumina joints were independently exposed to either oxidizing or reducing atmosphere at 800 °C for 100 h. Those samples that were thermally aged in air maintained good joint strength, similar to that of the original as-brazed samples. Microstructural analysis revealed no significant change in joint microstructure after long-term oxidation at elevated temperature, indicating excellent stability of the Ag–CuO-based filler metal in this environment. On the other hand, exposure of the air-brazed alumina joints to hydrogen under the same aging conditions resulted in a measurable decrease in joint strength. Scanning electron microscope analysis conducted on the fracture surfaces of the broken hydrogen-exposed specimens indicated that the source of joint failure was debonding along the interface between the filler metal and alumina substrate. This was due in large part to internal reduction of CuO precipitates within the filler metal to copper and accompanied by the simultaneous formation of porosity at these sites, both within the bulk of the joint as well as along the filler metal/substrate interfaces. Pore formation was noticeably present in filler metals prepared with a high concentration of copper oxide.

In this article, a novel pressureless solid-liquid reaction method is presented for preparation of yttrium disilicate (γ-Y2Si2O7). Single-phase γ-Y2Si2O7 powder was synthesized by calcination of SiO2 and Y2O3 powders with the addition of LiYO2 at 1400 °C for 4 h. The addition of LiYO2 significantly decreased the synthesis temperature, shortened the calcination time, and enhanced the stability of γ-Y2Si2O7. The sintering of these powders in air and O2 was studied by means of thermal mechanical analyzer. It is shown that the γ-Y2Si2O7 sintered in oxygen had a faster densification rate and a higher density than that sintered in air. Furthermore, single-phase γ-Y2Si2O7 with a density of 4.0 g/cm3 (99% of the theoretical density) was obtained by pressureless sintering at 1400 °C for 2 h in oxygen. Microstructures of the sintered samples are studied by scanning electron microscope.

Boron (B)-alloyed diamondlike carbon (B-DLC) films were prepared on polymethyl methacrylate (PMMA), glass, and silicon (100) using an inductive radio frequency Ar + C2H2 + B2H6 plasma immersion ion processing (PIIP) technique. The composition of the B-DLC films was measured by ion beam analysis techniques, and the bonding structure was characterized by infrared and Raman spectroscopy. The incorporation of B2H6 gas into the PIIP deposition introduced B-C bonds into the DLC structure, resulting in increased sp3-carbon bonding and improved optical performance. The energetic activation of the deposition atoms, induced by the ion bombardment during the PIIP film growth, enhanced the properties of the B-DLC films deposited on dielectric and transparent optical materials. With B-alloying and an optimized deposition energy of 40–135 eV, B-DLC films were synthesized with B-alloying up to 10.4 at.%, high hardness, high refractive index, and optical transmittance that is higher than that of unalloyed DLC films. The experimental results indicate that C-B hybridization and ion-energy transfer are critical to the synthesis of these hard and transparent B-DLC films.

HfB2–15 vol% MoSi2 composites were produced from powder mixtures and densified through different techniques, namely hot pressing and spark plasma sintering. Dense materials were obtained at 1900 °C by hot pressing and at 1750 °C by spark plasma sintering. Microstructure and mechanical properties were compared. The most relevant result was for high-temperature strength: independent of the processing technique, the flexural strength in air at 1500 °C was higher than 500 MPa.

Because of the applications for W/Cu composite materials in high technology, the advantages of synthesizing this alloy by the hydrogen reduction route were investigated, with special attention to the properties of the product that was formed. Kinetic studies of reduction indicated that the mechanism changes significantly at 923 K, and the product had unusual properties. In the present work, morphological studies of the W/Cu alloy with 20 wt% Cu, produced at 923 K, were carried out by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses. The structural studies performed by XRD indicated that, at 923 K, Cu dissolved in W, forming a metastable solid solution in the nanocrystalline state. The samples produced at higher as well as lower temperatures, on the other hand, showed the presence of two phases, pure W and pure Cu. The SEM results were in agreement with the XRD analysis and confirmed the formation of W/Cu alloy. TEM analysis results confirmed the above observations and showed that the particle sizes were about 20 nm. The structure of the W/Cu alloy produced in the present work was compared with those for pure Cu, produced from Cu2O produced by hydrogen reduction under similar conditions. This indicated that the presence of W hinders the coalescence of Cu particles, and the alloy retains its nano-grain structure. The present results open up an interesting process route toward the production of intermetallic phases and composite materials under optimized conditions.

Pr-doped ZnO phosphor powders were prepared by dry reaction within evacuated sealed silica glass tube. Pr2O3 and Pr6O11 were used as additives. Pr concentrations were 0.5, 1, 3, and 5 mol%, and the sintering temperatures were 600, 800, and 1000 °C, respectively. Photoluminescence (PL) and PL excitation (PLE) spectra were measured to study luminescent properties of samples. Some samples showed the enhancement of green emission. This emission is related to native defects in ZnO. Based on the results of PL and PLE, the origin of the enhancement was discussed in view of native defects in ZnO and the defect-related complex in ZnO varistor ceramics. The possible origin is the increase of native defects such as VZn, OZn, and the complex in the vicinity of grain boundaries and ZnO matrix near the surface of grains. The increase of native defects and the complex are probably due to the existence of the Pr3+-ions with binding to native defects, which form the complex by Coulombic potential.

Structural characterization at the nanometric scale of the Nautilus sp shell was carried out by high-resolution transmission electron microscopy and high-angle annular dark field to understand how the organic and inorganic components are related. The inorganic phase that built the shell is made of calcium carbonate (CaCO3), with the orthorhombic unit cell of the aragonite, in a texturized arrangement in such a way that the c-axis is always perpendicular to the shell surface. The organic material forms films through the plates. We observed for a very first time some aragonite nanocrystals embedded in the organic matrix. This observation supports the hypothesis that the proteins and other organic compounds guide the crystal growth because the organic matrixes are the places where the nanocrystals grow.

(Zr62Cu15.4Ni12.6) (x = 6–12) in situ glassy composites containing uniformly distributed Ta-rich particles were prepared by arc-melting and copper mould casting. The results show that addition of 6–10 at.% Ta to Zr62Cu15.4Ni12.6Al10 results in dissolution of 2.4 to 4.6 at.% Ta in the glassy matrix, which promotes glass-forming ability, and the remaining Ta precipitates out as body-centered cubic (BCC) Ta-rich particles dispersed on the glassy matrix. The critical diameters for the composites with 6, 8, and 10 at.% Ta are 7, 7, and 6 mm, respectively. At 12 at.% Ta addition, the glass-forming ability is dramatically reduced because of the precipitation of secondary dendritic Ta-rich particles and other nanocrystallites from melts during copper mould casting. Also, owing to the solid-liquid reaction during induction heating, some Ta-rich particles formed in the master alloys will redissolve into the glassy matrix, resulting in a smaller volume fraction of Ta-rich particles in the as-cast glassy rods than that of the corresponding ingots. The glassy matrix composites exhibit enhanced plastic strain of about 7.5 to 22.5% at room temperature. The optimum Ta content in the glassy alloys is determined to be 10 at.%, which corresponds to the highest ultimate stress of 2220 MPa and the largest plastic strain of 22.5%. The plastic strain increases with increasing volume fraction of in situ BCC Ta-rich particles. This is apparently ascribed to the impedance of Ta-rich particles to shear bands. Ta-rich particles seed the initiation of multiple shear bands and block the shear band propagation, leading to intensive multiplication and bifurcation of shear bands.

Hardness, elastic modulus, and stress directly influence the ability of tantalum carbide/amorphous hydrocarbon (TaC/a-C:H) thin films to enhance the wear-resistance of steel tribological component surfaces. Designed factorial experiments enabled an evaluation of the effects of acetylene flow rate (QC2H2), direct current bias voltage level (Vb), and substrate rotation rate (ωRot) during deposition on the mechanical properties of reactively sputtered TaC/a-C:H films. Significant relationships were found between compressive stress level and Vb, whereas hardness and elastic modulus were dependent primarily on Vb and secondarily on QC2H2 within the studied parameter space. It is proposed that effects of ion bombardment on the a-C:H phase during growth are responsible for property dependencies on Vb. Decreases in hardness and elastic modulus with increasing QC2H2 are attributed to increased hydrogen concentration and a concomitant decreased volume fraction of TaC crystallites in the films.